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Frequently Occurring Reconnection Jets from Sunspot Light Bridges
Tian, Hui,Yurchyshyn, Vasyl,Peter, Hardi,Solanki, Sami K.,Young, Peter R.,Ni, Lei,Cao, Wenda,Ji, Kaifan,Zhu, Yingjie,Zhang, Jingwen,Samanta, Tanmoy,Song, Yongliang,He, Jiansen,Wang, Linghua,Chen, Yaji American Astronomical Society 2018 The Astrophysical journal Vol.854 No.2
Kumar, Pankaj,Yurchyshyn, Vasyl,Wang, Haimin,Cho, Kyung-Suk IOP Publishing 2015 The Astrophysical journal Vol.809 No.1
<P>Using high-resolution images from the 1.6 m New Solar Telescope at Big Bear Solar Observatory, we report the direct evidence of chromospheric reconnection at the polarity inversion line between two small opposite polarity sunspots. Small jetlike structures (with velocities of similar to 20-55 km s(-1)) were observed at the reconnection site before the onset of the first M1.0 flare. The slow rise of untwisting jets was followed by the onset of cool plasma inflow (similar to 10 km s(-1)) at the reconnection site, causing the onset of a two-ribbon flare. The reconnection between two sheared J-shaped cool Ha loops causes the formation of a small twisted (S-shaped) flux rope in the chromosphere. In addition, Helioseismic and Magnetic Imager magnetograms show the flux cancellation (both positive and negative) during the first M1.0 flare. The emergence of negative flux and the cancellation of positive flux (with shear flows) continue until the successful eruption of the flux rope. The newly formed chromospheric flux rope becomes unstable and rises slowly with a speed of similar to 108 km s(-1) during a second C8.5 flare that occurred after similar to 3 hr of the first M1.0 flare. The flux rope was destroyed by repeated magnetic reconnection induced by its interaction with the ambient field (fan-spine topology) and looks like an untwisting surge (similar to 170 km s(-1)) in the coronal images recorded by the Solar Dynamics Observatory/Atmospheric Imaging Assembly. These observations suggest the formation of a chromospheric flux rope (by magnetic reconnection associated with flux cancellation) during the first M1.0 flare and its subsequent eruption/disruption during the second C8.5 flare.</P>
KINEMATICS OF SOLAR CHROMOSPHERIC SURGES OF AR 10930
봉수찬,조경석,Vasyl Yurchyshyn 한국천문학회 2014 Journal of The Korean Astronomical Society Vol.47 No.6
Solar chromospheric surges are often reported to contain rotational motion. However, thedetails of the motion and driving mechanism of the surges are not yet fully understood. Recurrent surgeswith rotational motion at AR 10930 on the west limb are observed by Hinode Solar Optical Telescope(SOT) continuously from 11:21 UT on December 18 to 09:58 UT on December 19, 2006, using the Ca ii Hbroadband filter. We analyze details of the motion including number of turns from the rise of the surge tothe fall, axial speed and acceleration. During the observation, rise and fall motion accompanying rotationappears recurrently. There occur a total of 14 surges at AR 10930 over 17 hours. The average durationis 45 minutes, and the average width, and length are 8 Mm, and 39 Mm, respectively. We speculate thatthe surges occurred by recurrent reconnections between the twisted prominence and large untwisted fluxtube.
SIMULTANEOUS OBSERVATION OF A HOT EXPLOSION BY NST AND IRIS
Kim, Yeon-Han,Yurchyshyn, Vasyl,Bong, Su-Chan,Cho, Il-Hyun,Cho, Kyung-Suk,Lee, Jaejin,Lim, Eun-Kyung,Park, Young-Deuk,Yang, Heesu,Ahn, Kwangsu,Goode, Philip R.,Jang, Bi-Ho IOP Publishing 2015 The Astrophysical journal Vol.810 No.1
<P>We present the first simultaneous observations of so-called 'hot explosions' in the cool atmosphere of the Sun made by the New Solar Telescope (NST) of Big Bear Solar Observatory and the Interface Region Imaging Spectrograph (IRIS) in space. The data were obtained during the joint IRIS-NST observations on 2014 July 30. The explosion of interest started around 19: 20 UT and lasted for about 10 minutes. Our findings are as follows: (1) the IRIS brightening was observed in three channels of slit-jaw images, which cover the temperature range from 4000 to 80,000 K; (2) during the brightening, the Si IV emission profile showed a double-peaked shape with highly blue and redshifted components (-40 and 80 km s(-1)); (3) wing brightening occurred in H alpha and Ca II 8542 angstrom bands and related surges were observed in both bands of the NST Fast Imaging Solar Spectrograph (FISS) instrument; (4) the elongated granule, seen in NST TiO data, is clear evidence of the emergence of positive flux to trigger the hot explosion; (5) the brightening in Solar Dynamics Observatory/Atmospheric Imaging Assembly 1600 angstrom images is quite consistent with the IRIS brightening. These observations suggest that our event is a hot explosion that occurred in the cool atmosphere of the Sun. In addition, our event appeared as an Ellerman bomb (EB) in the wing of H alpha, although its intensity is weak and the vertical extent of the brightening seems to be relatively high compared with the typical EBs.</P>
Lim, Eun-Kyung,Yurchyshyn, Vasyl,Kumar, Pankaj,Cho, Kyuhyoun,Jiang, Chaowei,Kim, Sujin,Yang, Heesu,Chae, Jongchul,Cho, Kyung-Suk,Lee, Jeongwoo American Astronomical Society 2017 The Astrophysical journal Vol.850 No.2
<P>Solar flare ribbons provide an important clue to the magnetic reconnection process and associated magnetic field topology in the solar corona. We detected a large-scale secondary flare ribbon of a circular shape that developed in association with two successive M-class flares and one coronal mass ejection. The ribbon revealed interesting properties such as (1) a quasi-circular shape and enclosing the central active region (AR); (2) the size as large as 500 '' by 650 ''; (3) successive brightenings in the clockwise direction at a speed of 160 km s(-1) starting from the nearest position to the flaring sunspots; (4) radial contraction and expansion in the northern and the southern part, respectively, at speeds of <= 10 km s(-1). Using multi-wavelength data from Solar Dynamics Observatory, RHESSI, XRT, and Nobeyama, along with magnetic field extrapolations, we found that: (1) the secondary ribbon location is consistent with those of the field line footpoints of a fan-shaped magnetic structure that connects the flaring region and the ambient decaying field; (2) the second M2.6 flare occurred when the expanding coronal loops driven by the first M2.0 flare encountered the background decayed field; (3) immediately after the second flare, the secondary ribbon developed along with dimming regions. Based on our findings, we suggest that interaction between the expanding sigmoid field and the overlying fan-shaped field triggered the secondary reconnection that resulted in the field opening and formation of the quasi-circular secondary ribbon. We thus conclude that interaction between the AR and the ambient large-scale fields should be taken into account to fully understand the entire eruption process.</P>
OBSERVATION OF A NON-RADIAL PENUMBRA IN A FLUX EMERGING REGION UNDER CHROMOSPHERIC CANOPY FIELDS
Lim, Eun-Kyung,Yurchyshyn, Vasyl,Goode, Philip,Cho, Kyung-Suk IOP Publishing 2013 ASTROPHYSICAL JOURNAL LETTERS - Vol.769 No.1
<P>The presence of a penumbra is one of the main properties of a mature sunspot, but its formation mechanism has been elusive due to a lack of observations that fully cover the formation process. Utilizing the New Solar Telescope at the Big Bear Solar Observatory, we observed the formation of a partial penumbra for about 7 hr simultaneously at the photospheric (TiO; 7057 angstrom) and the chromospheric (H alpha - 1 angstrom) spectral lines with high spatial and temporal resolution. From this uninterrupted, long observing sequence, we found that the formation of the observed penumbra was closely associated with flux emergence under the pre-existing chromospheric canopy fields. Based on this finding, we suggest a possible scenario for penumbra formation in which a penumbra forms when the emerging flux is constrained from continuing to emerge, but rather is trapped at the photospheric level by the overlying chromospheric canopy fields.</P>
Chromospheric Plasma Ejections in a Light Bridge of a Sunspot
Song, Donguk,Chae, Jongchul,Yurchyshyn, Vasyl,Lim, Eun-Kyung,Cho, Kyung-Suk,Yang, Heesu,Cho, Kyuhyoun,Kwak, Hannah American Astronomical Society 2017 The Astrophysical Journal Vol.835 No.2
<P>It is well-known that light bridges (LBs) inside a sunspot produce small-scale plasma ejections and transient brightenings in the chromosphere, but the nature and origin of such phenomena are still unclear. Utilizing the high-spatial and high-temporal resolution spectral data taken with the Fast Imaging Solar Spectrograph and the TiO 7057 angstrom broadband filter images installed at the 1.6 m New Solar Telescope of Big Bear Solar Observatory, we report arcsecond-scale chromospheric plasma ejections (1.'' 7) inside a LB. Interestingly, the ejections are found to be a manifestation of upwardly propagating shock waves as evidenced by the sawtooth patterns seen in the temporal-spectral plots of the Ca II. 8542 angstrom and Ha intensities. We also found a fine-scale photospheric pattern (1 '') diverging with a speed of about 2 km s(-1) two minutes before the plasma ejections, which seems to be a manifestation of magnetic flux emergence. As a response to the plasma ejections, the corona displayed small-scale transient brightenings. Based on our findings, we suggest that the shock waves can be excited by the local disturbance caused by magnetic reconnection between the emerging flux inside the LB and the adjacent umbral magnetic field. The disturbance generates slow-mode waves, which soon develop into shock waves, and manifest themselves as the arcsecond-scale plasma ejections. It also appears that the dissipation of mechanical energy in the shock waves can heat the local corona.</P>